We propose to develop a series of cyclic and otherwise conformationally restricted peptide analogues which have high receptor specificity, high agonist or antagonist biological activities, high stability in vivo, and prolonged in vitro activity for mu and kappa opioid receptors. For this purpose, we have developed a multidisciplinary approach combining modern synthetic organic amino acid and peptide chemistry, conformational analysis and peptide drug design, with biochemical, biophysical, physiological, and behavioral pharmacology. Using this approach we will develop structure- and conformation-biological activity relationships and insights which will lead to compounds with specific agonist and antagonist activities at mu and kappa opioid receptors. Specific aims include: a) continued development of cyclic, conformationally constrained peptides (derived from somatostatin) with high mu opioid receptor specificity and potency and opioid antagonist activity; b) design, synthesis, and evaluation of novel peptides derived from dynorphin and Alpha-neoendorphin with high kappa opioid receptor potency and specificity; c) careful evaluation of the conformational and dynamic properties of selected analogues to determine the biophysical basis for their biological activity and to aid in the development of a rational approach to more specific and/or potent compounds; d) to evaluate the peptides we design and synthesize for specific binding to mu, delta, kappa, and sigma opioid receptors in the brain; to localize the binding sites in the brain for highly selective radiolabeled analogues; e) to comprehensively evaluate activities in vitro using the guinea pig ileum, mouse vas deferens, rabbit vas deferens, hamster vas deferens, and other assays to establish receptor specificity and to aid in the development of new, more potent and selective analogues; f) to carefully evaluate mu and kappa activities of new compounds in vivo using the rat urinary bladder model (mu receptor) and the mouse abdominal stretch (kappa receptor) test after IT administration; and g) to examine mu, delta, and kappa receptor specific analogues for activity at the PCP/sigma receptor system in the brain using the radioligand (3H)TCP; structure-function analysis of the natural endogenous PCP/sigma polypeptide (once its structure has been determined) will be examined. The long term goal of this research is to develop an understanding of the physiological roles of the various opioid receptors, and to develop ligands for these receptors which can be used for the treatment of disease.